Existing techniques for mixing particles of different sizes include fluidization, single or double rain mixing, or the use of high shear mixing equipment. Some of these techniques are associated with disadvantages and can present additional problem when applied to delicate particles that are prone to attrition.
Fluidization, for instance, provides good mixing but can result in segregation and elutriation of small particles. Single rain methods, in which the smaller particles fall by gravity (rain) on top of the larger particles, tend to give poor results when used to mix aerogel particles of different sizes. Double rain mixing, which refers to letting both the coarse and fine particles fall by gravity (settle together), requires complicated and time consuming set up arrangements. Particle attrition can be a major drawback for using high shear mixing equipment
Conventionally packed coarse aerogel beads of about 2-3 mm can exhibit interparticle void spaces, often as high as 50%. The voids lower the insulating properties of these materials.